wallet: fix coin selection tracing to return -1 when no change pos

2 files changed, 25 insertions, 2 deletions

diff --git a/src/wallet/spend.cpp b/src/wallet/spend.cpp
index b51cd6332f..5b464ae3f5 100644
--- a/src/wallet/spend.cpp
+++ b/src/wallet/spend.cpp
@@ -1337,7 +1337,7 @@ util::Result<CreatedTransactionResult> CreateTransaction(
 
     auto res = CreateTransactionInternal(wallet, vecSend, change_pos, coin_control, sign);
     TRACE4(coin_selection, normal_create_tx_internal, wallet.GetName().c_str(), bool(res),
-           res ? res->fee : 0, res && res->change_pos.has_value() ? *res->change_pos : 0);
+           res ? res->fee : 0, res && res->change_pos.has_value() ? int32_t(*res->change_pos) : -1);
     if (!res) return res;
     const auto& txr_ungrouped = *res;
     // try with avoidpartialspends unless it's enabled already
@@ -1355,7 +1355,7 @@ util::Result<CreatedTransactionResult> CreateTransaction(
         // if fee of this alternative one is within the range of the max fee, we use this one
         const bool use_aps{txr_grouped.has_value() ? (txr_grouped->fee <= txr_ungrouped.fee + wallet.m_max_aps_fee) : false};
         TRACE5(coin_selection, aps_create_tx_internal, wallet.GetName().c_str(), use_aps, txr_grouped.has_value(),
-               txr_grouped.has_value() ? txr_grouped->fee : 0, txr_grouped.has_value() && txr_grouped->change_pos.has_value() ? *txr_grouped->change_pos : 0);
+               txr_grouped.has_value() ? txr_grouped->fee : 0, txr_grouped.has_value() && txr_grouped->change_pos.has_value() ? int32_t(*txr_grouped->change_pos) : -1);
         if (txr_grouped) {
             wallet.WalletLogPrintf("Fee non-grouped = %lld, grouped = %lld, using %s\n",
                 txr_ungrouped.fee, txr_grouped->fee, use_aps ? "grouped" : "non-grouped");
diff --git a/test/functional/interface_usdt_coinselection.py b/test/functional/interface_usdt_coinselection.py
index aff90ea5fc..30931a41cd 100755
--- a/test/functional/interface_usdt_coinselection.py
+++ b/test/functional/interface_usdt_coinselection.py
@@ -204,6 +204,29 @@ class CoinSelectionTracepointTest(BitcoinTestFramework):
         assert_equal(success, True)
         assert_equal(use_aps, None)
 
+        self.log.info("Change position is -1 if no change is created with APS when APS was initially not used")
+        # We should have 2 tracepoints in the order:
+        # 1. selected_coins (type 1)
+        # 2. normal_create_tx_internal (type 2)
+        # 3. attempting_aps_create_tx (type 3)
+        # 4. selected_coins (type 1)
+        # 5. aps_create_tx_internal (type 4)
+        wallet.sendtoaddress(address=wallet.getnewaddress(), amount=wallet.getbalance(), subtractfeefromamount=True, avoid_reuse=False)
+        events = self.get_tracepoints([1, 2, 3, 1, 4])
+        success, use_aps, algo, waste, change_pos = self.determine_selection_from_usdt(events)
+        assert_equal(success, True)
+        assert_equal(change_pos, -1)
+
+        self.log.info("Change position is -1 if no change is created normally and APS is not used")
+        # We should have 2 tracepoints in the order:
+        # 1. selected_coins (type 1)
+        # 2. normal_create_tx_internal (type 2)
+        wallet.sendtoaddress(address=wallet.getnewaddress(), amount=wallet.getbalance(), subtractfeefromamount=True)
+        events = self.get_tracepoints([1, 2])
+        success, use_aps, algo, waste, change_pos = self.determine_selection_from_usdt(events)
+        assert_equal(success, True)
+        assert_equal(change_pos, -1)
+
         self.bpf.cleanup()